Defrost the lamb by putting it in your fridge the night before or the morning of the day you’d like to cook it. Finely dice the onion and mix it with the ground lamb; season generously with salt and pepper and a pinch of chili flakes. Form the lamb into four small patties. Heat a skillet over medium-high heat. Place the patties in a dry skillet, there is enough natural fat to cook the burgers. Sear for three minutes per side until they are medium rare. Finely dice the cherry tomatoes and radish. Chop the mint and garlic finely. Combine those four ingredients together with the yogurt, red wine vinegar and cumin, if using. Season with salt and pepper and adjust the level of vinegar and cumin to your liking. Serve the lamb burgers over greens with a generous dollop of yogurt sauce.